Switching Communication Baud Rate

This entry was posted on July 12, 2010 by ScanTool.net Team.

This article describes two methods for changing the communication baud rate. Method 1 is the "safe" method, however it requires firmware v2.0.1 or higher. Method 2 works with older OBDLink firmware, as well as the ElmScan 5 ELM327-based interfaces. However it must be used with caution, as it allows the baud rate to be set to a value not supported by the communication channel in use.

Note that the baud rate can be set to the same baud rate as the current baud rate. This may be useful when you want to ensure that the baud rate remains the same when you reflash OBDLink with different firmware. For example, if you don't explicitly set the baud rate to 38400 for a unit that currently has v1.2.4 and upgrade it to v2.1.0, the default baud rate would change from 38400 to 115200 bps.

Please remember that most diagnostic software supports a limited, fixed set of baud rates. Be sure that when you change the baud rate, the new baud rate is supported by your favorite software.

Method 1: STSBR

Connect to the scan tool using a terminal emulator (for example, HyperTerminal, TeraTerm, or STNTerm) at 115200 bps.

Enter STSBR followed by the new baud rate, for example:
STSBR 38400

Switch the terminal emulator to the new baud rate, and send the STI command to ensure that communication is possible at the new baud rate. You should get a response similar to this:STN1101 v2.1.0

Enter STWBR to save the new baud rate.

Method 2: AT PP 0C

This method works on firmware v1.1.0 and above, as well as all ELM327-based interfaces. Be extra careful when using this method, as it lets you set the baud rate outside the range supported by the hardware.

Connect to the scan tool using a terminal emulator (for example, HyperTerminal, TeraTerm, or STNTerm) at the current baud rate.

Enter the following commands, terminating each one with an 'Enter':

ATPP 0C SV xxATPP 0C ON
ATZ
Here are some of the common baud rates and the corresponding values for xx:

Baud Rate (kbps)

xx

19.2

D0

38.4

68

57.6

45

115.2

23

230.4

11

500

08

For example, to set the baud rate to 115200 bps, you would enter:

ATPP 0C
SV 23
ATPP 0C ON
ATZ

Switch the terminal emulator to the new baud rate, and enter the ATI command to test communication at the new baud rate. The scan tool response would look similar to this: